The Committee didn't announce why the representatives are under investigation, although the Office of Congressional Ethics (OCE) has recommended a full investigation into all four. Bachmann, who won't seek reelection and has been under investigation for her campaign finances, had her investigation extended. It's unclear as to why the three other members are being investigated.

"The Committee notes that the mere fact of a referral or an extension, and the mandatory disclosure of such an extension and the name of the subject of the matter, does not itself indicate that any violation has occurred, or reflect any judgment on behalf of the Committee," a statement from the chairman and ranking member said for all four members.

The OCE started investigating Bachmann following her run for president and her 2011 book tour. "Federal election and House ethics rules generally forbid candidates from using campaign funds or resources to sell or promote their own books, which are considered personal business activities," the Star Tribune reported.

William McGinley, Bachmann's attorney, has denied the allegations against the representative. “We are confident the Committee will discover, upon proper review, that the highly politicized allegations made at the OCE level were baseless and without merit,” McGinley wrote in an email to the Washington Post.

More information on the investigations will be released by Sept. 11, according to the statement from the chairman and ranking member of the House Ethics Committee.